Yoong-Ho Jung

Various design techniques to reduce cogging torque by controlling energy variation in permanent magnet motors

Using energy method, this paper analytically reveals that the cogging torque can be reduced by controlling N/sub L/th harmonic components of the square of airgap permeance function and flux density function, where N/sub L/ denotes the least common multiple of number of poles and number of slots. As for design tools, it introduces various design techniques to reduce cogging torque with analytical formulation and FEM examples.

Comparison of magnetic forces for IPM and SPM motor with rotor eccentricity

The permanent magnet motor is often the most important element in many precision rotor applications and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper investigates radial force density and magnetic unbalanced force for IPM and SPM motors when rotor eccentricity exists. For the magnetic field analysis, a finite element method is used to account for the magnetic saturation and rotor eccentricity. The radial force density and magnetic unbalanced force are analyzed by Maxwell stress tensor and discrete Fourier transform. An IPM BLDC motor, mostly chosen to realize high speed operation, is significantly affected by rotor eccentricity due to magnetic saturation.

Comparison of vibration sources between symmetric and asymmetric HDD spindle motors with rotor eccentricity

The permanent magnet motor is often the most important element in hard disk drive (HDD) spindles and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper analytically discusses effects of rotor eccentricity on motor performances for symmetric and asymmetric motors, such as local traction, unbalanced force, cogging torque, back EMF, phase current and torque ripple. An asymmetric motor, mostly chosen to reduce the cogging torque, shows a worse effect on cogging torque and unbalanced force when the eccentricity exists. It also adversely affects the flux linkage and introduces variation of the phase back EMF depending on winding and rotating eccentricity, thus yielding increased mutual torque ripple.

Chip load prediction in ball-end milling

Abstract In the modern manufacturing of sophisticated parts with 3D sculptured surfaces such as dies and molds, ball-end milling is one of the most widely used machining processes to remove unwanted material. However, the machining processes are accompanied by cutting forces that cause tool chattering and dimensional errors. In this paper, a calculation algorithm for the chip load along the cutting edge is proposed, so that it is can be used for predicting cutting forces and the region with excessive dimensional error in the ball-end milling process. For this purpose, an exact chip engagement surface (ECES) from cutting edge geometry is suggested to be a mathematical model with the feed rate effect of cutter, instead of a semi-spherical surface. With the calculated chip load distribution, a simplified method for calculating cutting force at a cutter location is also proposed.

A study on micro-grooving characteristics of planar lightwave circuit and glass using ultrasonic vibration cutting

Abstract Micro-grooving of brittle materials such as glass, which are widely used as optical components, was accomplished using a polycrystalline diamond tool with ultrasonic vibration. To determine the cutting characteristics of brittle materials, the machining system with an ultrasonic vibration tool was built. Experiments for micro-grooving of the planar lightwave circuits (PLCs) and glass were performed and their shapes were measured by microscopic photograph. Better groove shapes with low chipping of PLCs and glass were obtained by ultrasonic vibration cutting. These experiments are considered as a possibility for micro-grooving of optical communication components.

The Influence of Electromagnetic Force Upon the Noise of an IPM Motor Used in a Compressor

Recent power electronics and control technology have equipped air conditioners with additional functions such as air purification and energy saving, however, the noise and vibration originating with the compressor still remains to be improved. The interior permanent magnet (IPM) motor has become the compressor drive motor of choice became of the need for small high-powered compressors. Due to the structural peculiarity of IPM, it generates not only magnetic torque, but also reluctance torque which helps to achieve high power density while aggravating the noise problem. In this study the influences of natural frequencies and mode shapes of the structures were investigated to reduce the noise and vibration of an IPM motor. For better understanding of noise source, electromagnetic force has to be analyzed and this papers deals with noise problem caused only by electromagnetic force

An experimental study on the performance of a condensing tumbler dryer with an air-to-air heat exchanger

The performance of energy consumption in the closed-loop tumbler dryer with a condenser for clothes drying is evaluated as a function of the heater capacity, the drying air flow rate inside the dryer, and the cooling air flow rate. The clothes dryer in laundries used in this study consists of a tumbling drum, condenser for condensing the humid and hot air flowing out the rotating drums, and electric heater for heating the circulating drying air. Tests were performed at the heating capacity of 1.9 kW to 2.7 kW, the drying air flow rate of 60 m3/h to 140 m3/h, and the cooling air flow rate of 100 m3/h to 240 m3/h. The total energy consumption, the drying time, and the condensate water rate were also investigated. Parametric results showed that a larger heater power resulted in shorter drying time. With increasing heater power, the air temperature and the condensate rate increased due to the higher humidity ratio in the air. The drying air flow rate and the cooling air flow rate did not have a significant effect on drying performance.

Shape design of efficient retroreflective articles

Abstract Retroreflective article is different from other reflecting objects as it returns the incident ray back to the source. This characteristic makes the retroreflectors have many applications in reflective highway signs, reflective vests, and other safety-related items. These articles may have various shapes. However, the quantitative evaluation of performance for the best shape of retroreflector needs much time and cost for manufacturing prototypes and for performance experiments. In this work, we have developed a program for simulating the trace of ray entered into a retroreflective element, in order to determine the optimal shape of retroreflection. We have also proposed new performance criterion of retroreflective articles, which can consider the range of incident angle (RIA), instead of the criterion with the merely retroreflective strength.

Attaching single carbon nanotube on tip's apex using dielectrophoresis of DC-pulse voltage

Abstract Single carbon nanotubes (CNTs) are candidates for a number of electronics and sensing applications, provided that single CNTs can be separated from a bundle of CNTs in suspension. Dielectrophoresis has recently been demonstrated as one route for the extraction of desired CNTs. However, previous methods using dielectrophoresis have found it difficult to extract single nanotubes from bundles of CNTs in solution. Here, we show that this restriction can be overcome by using pulsed DC voltage of an electric field, instead of regular AC and DC voltages.

Swept volume with self-intersection for five-axis ball-end milling

Abstract The generation of a volume swept by a tool along its path, called the swept volume, is indispensable for the volumetric simulation of five-axis machining. In some cases of five-axis machining, the swept volume may be self-intersecting, which requires special processing to handle the geometric and topological problems due to complex tool motion. In this work, an algorithm is proposed for generating the swept volume, including the self-intersection case for five-axis ball-end milling, based on triangle strip representation. The proposed algorithm has various applications such as interference detection in assembly design, and visualization of manipulator motions in robotics.